[SYCL-MLIR] Opaque pointer support Polygeist-to-LLVM

[sommerlukas]

First step to add opaque pointer support for the SYCL-MLIR project: Make the lowering patterns in the Polygeist-to-LLVM lowering compatible with opaque pointers.

Partly resolves #8616.

[sommerlukas]

I did not want to migrate all our components to opaque pointers in a single step, as the resulting PR would be huge. Instead, this is the first step, affecting only the Polygeist to LLVM lowering.

As some of the patterns are shared with other lowerings and other tests/components still rely on this lowering to produce typed pointers, I had to introduce a "versioning". The existing patterns now have a "Old" suffix, and the patterns with the unmodified name have been changed to support opaque pointers. The polygeist-to-llvm pass additionally supports a use-opaque-pointers option (defaulting to false), so it can continue to produce typed pointers when other parts rely on that (e.g. cgeist).

The patterns (and functions) with the "Old" suffix as well as the option can be removed as soon as we complete the transition to opaque pointers. They are unmodified compared to sycl-mlir, so do not need to be reviewed.

Having the versioning and option also allow us to continue to produce typed pointers, in case other tools out-of-scope of this project (e.g., SPIR-V translator) still need to complete the transition.

The LIT tests for the Polygeist to LLVM lowering already verify the correctness of the opaque pointer version.

[victor-eds]

Can we have the pointee type in all check lines with GEPOp operations?

[sommerlukas]

I assume CI will currently failed, as I have rebased on top of #8774 and the branch is currently still missing the fix from #8817. Will need to rebase again once #8817 has been merged.

[sommerlukas]

I assume CI will currently failed, as I have rebased on top of #8774 and the branch is currently still missing the fix from #8817. Will need to rebase again once #8817 has been merged.

Rebased now that #8817 has been merged.